Where are the best spots to jack up the front end on a 300E so I can get underneath the car

 

While you didn't indicate the MY, all of myMBs have only had jack points on the side of the car; one behind the front wheel and one in front of the rear wheel.
Another option is tire ramps that you drive up on.
In either situation, make sure you block the remaining tires and use a secondary safety block in case your jacks fails at an inappropriate time.

 

isnt it around the axle?

 

I wouldn't suggest lifting anywhere near the axle. The jack points are on the side rocker panels. You can see them clearly if you look just a few inches past the front wheel and the second one is a few inches in front of the rear wheel. Even the MB dealer hoists the car using the same jack points.